The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, the semiconductor industry utilized various methods and structures to form pulse width modulated (PWM) power supply controllers that were used to regulate an output voltage of a power supply system. Most PWM power supply controllers included a soft-start function that, during the initial startup, slowly increased the maximum current that was used to regulate the output voltage. Another function that was generally included in most PWM power supply controllers was a burst mode or skip cycle mode. The burst mode or skip cycle mode was used to decrease power dissipation and improve voltage regulation when the power requirements of load decreased to a light level. One example of such a power supply controller was the NCP1239 that was available from ON semiconductor of Phoenix Arizona.
In most cases, when the power supply controller transitioned from the skip cycle mode to the normal operating mode, the soft-start function was re-enabled to slowly increase the maximum current that was supplied to the load. In some cases, during the transition the output voltage generally would undershoot and take a long time to reach the desired regulated output voltage value.
Accordingly, it is desirable to have a power supply controller that has both a soft-start function and a skip cycle function and that does not undershoot the output voltage when transitioning from the skip cycle operating mode to the normal operating mode.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay between the reaction that is initiated by the initial action.